New axis-marking method for a toric intraocular lens: mapping method

Abstract

Purpose: A new axis-marking method, the mapping method, for toric intraocular lens (IOL) implantation is described, and its accuracy is compared with that of conventional methods.

Methods: For toric IOL implantation, the steepest corneal axis was determined by IOLMaster optical biometer measurement (Carl Zeiss Meditec). Three marking methods for accurate alignment of the IOL astigmatism axis to the steepest corneal axis were evaluated and compared. For method 1, the patient was seated at the surgical table and instructed to gaze at a distant target. Using a toric reference marker, the corneal limbus was marked at the 3-, 6-, and 9-o'clock positions. The goal axis was also marked using a toric axis marker. Method 2 used a horizontal slit beam for reference marking points at 3 and 9 o'clock. Method 3 was the new mapping method, in which an anterior segment photograph was used to identify several reference vessel points and axis marking points and to calculate actual lengths from the reference vessel points to the axis marking points. During surgery, the axis marking points were marked on the limbus of the eye using calipers. The accuracy of the three axis-marking methods was evaluated using anterior segment photographs.

Results: With method 1, the average axis-marking error was 3.69±1.49°. With method 2, the average axis-marking error was 3.14±1.64°. With method 3, the new mapping method, the average axis-marking error was 2.29±1.06°. The new mapping method was more accurate than methods 1 and 2 (P<.01 and P=.016, respectively, paired t test). Axis-marking errors of the two conventional methods were not significantly different (P=.061).

Conclusions: The new axis-marking method, which uses distinct conjunctival vessels as a reference point, showed less axis-marking error compared to the conventional methods examined in this study.